In order to accurately reproduce sound based on input audio signals, a loudspeaker must be capable of precisely generating sound for a wide range of frequencies of the input audio signals. For example, input audio signals corresponding to musical songs have a wide range of frequencies relating to the various instruments creating the music and relating to the human vocal sounds corresponding to the lyrics that accompany the music. Thus, to accurately reproduce the audio signals, the loudspeaker generally has at least a main speaker cone for reproducing the low and mid-range frequencies of the audio signals. Furthermore, since the main speaker cone cannot effectively reproduce high frequency sounds, a whizzer cone has been developed for reproducing the high range frequencies of the audio signals. Typically, in the loudspeaker, the transition between the main speaker cone operation and the whizzer cone operation occurs when the frequencies of the audio signals reach between 4000 Hz and 8000 Hz.
An example of a whizzer cone 1 that reproduces high frequency sounds is illustrated in FIGS. 1a and 1b. FIG. 1a is a side view of the whizzer cone 1, and FIG. 1b is a top view of the whizzer cone 1. As shown in the figures, the whizzer cone 1 comprises a base portion 2 having a front end 3 and a rear end 4. The front end 3 generally has a circular shape and lies within a single plane. Similarly, the rear end 4 generally has a circular shape, which is concentric with the circular shape of the front end 3, but the diameter of the rear end 4 is smaller than the diameter of the front end 3. Also, the base portion generally has a frustro-conical shape having a circular cross-section, and the diameter of the cross-section of the base portion 2 gradually increases from the rear end 4 to the front end 3.
Also, as best shown in FIG. 1b, a rear wall 5 is formed at the rear end 4 of the base portion 2, and the circular front end 3 defines an opening to the base portion 2. Sound is generated from the vibration of the whizzer cone 1, and the vibration generally travels from the rear end 4 and/or rear wall 5 and is radiated from the whizzer cone 1. On the other hand, if the whizzer cone 1 is attached to a loudspeaker at an attachment point other than the rear end 4 and/or rear wall 5, the vibration generally travels from the attachment point and is radiated from the whizzer cone 1.
FIG. 2 illustrates an example of cross-sectional view of a loudspeaker 10 that comprises the whizzer cone 1 shown in FIGS. 1a and 1b. As shown in the figure, the loudspeaker 10 comprises the whizzer cone 1, a main speaker cone 12 having a flexible rim portion 14, a chassis 16, and a voice coil former 18. The coil former 18 is formed in a rear portion 16a of the chassis 16, and the whizzer cone 1 is fitted into a front opening 18a of the coil former 18. In addition, a rear end 12a of the main speaker cone 12 is fitted around the front opening 18a of the coil former 18, and the rim portion 14 of the speaker cone 12 is coupled to a front portion 16b of the chassis 16. Although the whizzer cone 1 is incorporated into the loudspeaker 10 by fitting it within the front opening 18a of the coil former 18, one skilled in the art, upon reading the present application, would clearly know many different manners in which the whizzer cone 1 could be incorporated into the loudspeaker 10. For example, the whizzer cone 1 could be attached to the main speaker cone 12 instead of the voice coil former 18.
Based on the configuration above, when audio signals having low to mid-range frequencies are input to the loudspeaker 10, the main speaker cone 12 responds to such signals and vibrates to reproduce corresponding sounds. On the other hand, when audio signals having high range frequencies are input to the loudspeaker 10, the whizzer cone 1 responds to such signals and vibrates to reproduce corresponding sounds. Furthermore, as noted above, the main speaker cone 12 ceases reproducing sounds and the whizzer cone 1 begins to reproduce sounds when the frequency of the audio signals reach a frequency between 4000 Hz and 8000 Hz. Accordingly, by incorporating the whizzer cone 1 into the loudspeaker 10, the loudspeaker is capable of reproducing sounds corresponding to a wide range of audio signal frequencies.
However, the loudspeaker 10 described above suffers from several disadvantages. For example, in the loudspeaker 10, the outer edge of the main speaker cone 12 is damped because it is physically coupled to the front portion 16b of the chassis 16 via the rim portion 14. On the other hand, the front end 3 of the whizzer cone 1 is not connected to any portions of the loudspeaker 10. As a result, the geometric modes at occurring near the front end 3 of the whizzer cone 1 are undamped and create irregularities in the frequency response of the whizzer cone 1. One of the most noticeable irregularities is the occurrence of sharp dips in the frequency response of the whizzer cone 1 at certain frequencies (“dip frequencies”) or certain ranges of frequencies (“dip frequency ranges”). In other words, when an audio signal is input to the loudspeaker 10 which has one of the certain frequencies or has a frequency that falls within one of the certain ranges of frequencies, the whizzer cone 1 cannot accurately reproduce a sound corresponding to the audio signal. Typically, the damaging dip frequencies of the whizzer cone 1 occur between 10,000 Hz and 20,000 Hz.
A graphical example of the dip 30 in the responsiveness of the whizzer cone 1 is shown in FIG. 3. As clearly shown in the figure, as the dip 30 becomes deeper and/or wider, the performance quality of the loudspeaker 10 decreases.
In addition to sharp dips, irregularities in the frequency response of the whizzer cone 1 may take the form of sharp peaks in the frequency response at certain frequencies (“peak frequencies”) or certain ranges of frequencies (“peak frequency ranges”). As the name implies, a peak is a sharp rise in the frequency response of the whizzer cone 1. Moreover, as a peak becomes taller and/or wider, the performance quality of the loudspeaker 10 decreases.
Some techniques have been developed to attempt overcome the above problem. For example, in one technique, the dips and peaks in the responsiveness of the whizzer cone 1 have been reduced by optimizing the dimensions of the whizzer cone 1 and the properties of the materials forming the whizzer cone 1. However, while such technique has somewhat reduced the frequency response irregularities of the whizzer cone 1, such irregularities are still very prominent, and the performance quality of the loudspeaker is still relatively low.